Fleck wrote that the development of truth in scientific research was an unattainable ideal as different researchers were locked in thought collectives (or thought-styles). He felt that the development of scientific insights was not unidirectional and does not consist of just accumulating new pieces of information, but also in overthrowing the old ones. This approach is now known as social constructionism.

Fleck was born in L'viv (Lwow), and grew up in the cultural autonomy of Austrian province of Galicia. He graduated from the Polish Lyceum in 1914 and he enrolled at the Jan Kazimierz University of L'viv, where he received his medical degree. In 1920 he became an assistant of the famous typhus specialist Rudolf Weigl when he was appointed to the chair in Biology at the University of L'viv in 1921. From 1923 to 1935 he worked firstly in the Department of Internal Medicine of the General Hospital in L'viv and then became Director of the Bacteriological Laboratory of the local social assurance authority. From 1935 he worked in the private bacteriological laboratory which he had earlier founded.

With Nazi Germany's occupation of L'viv, Fleck was deported with his wife, Ernestina Waldman, and son Ryszard to the city's Jewish ghetto. He continued his research in the hospital and developed a new procedure in which he procured vaccine from the urine of typhus patients. Fleck's work was known to the German occupiers and his family were arrested in December 1942 and deported to the Laokoon" pharmaceutical factory to produce typhus serum. He and his family were arrested again and sent to the Auschwitz concentration camp on February 7 1943. His task was to diagnose syphilis, typhus and other illnesses using serological tests. From December 1943 until the liberation of Poland on April 11, 1945 Fleck was detained in Buchenwald concentration camp.

Between 1945 and 1952, he served as the head of the Institute of Microbiology of the School of Medicine of Maria Sklodowska-Curie University of Lublin. In 1952, he moved to Warsaw to become the Director of the Department of Microbiology and Immunology at the Mother and Child State Institute. In 1954 he was elected a member of the Polish Academy of Sciences. Fleck's research during these years focused on the question of the behavior of leucocytes in infectious and stress situations. Between 1946 and 1957 he published 87 medical and scientific articles in Polish, French, English and Swiss journals. In 1951 Fleck was awarded the National Prize for Scientific Achievements and in 1955 the Officer's Cross of the Order of the Renaissance of Poland.

In 1956, after a heart attack and the discovery that he was suffering from lymphosarcoma, Fleck emigrated to Israel where a position was created for him at the Israel Institute for Biological Research. He died in 1961 at the age of 64 of a second heart attack.

The Ludwig Fleck Prize is awarded annually for the best book in the area of science and technology studies. It was created by the 4S Council (Society for the Social Studies of Science) in 1992.

The Genesis and Development of a Scientific Fact, (edited by T.J. Trenn and R.K. Merton, foreword by Thomas Kuhn) Chicago: University of Chicago Press, 1979. This is the first English translation of his 1935 book titled Entstehung und Entwicklung einer wissenschaftlichen Tatsache. Einführung in die Lehre vom Denkstil und Denkkollektiv Schwabe und Co., Verlagsbuchhandlung, Basel.